meat/app/level.ts

import { Color } from "../engine/render/Color"
import type { CloudLayer, SkyConfig } from "../engine/render/Sky"
import type { Mesh } from "../engine/scene/Mesh"
import { Terrain } from "../engine/scene/Terrain"

type Corner = [number, number, number]

/** Axis-aligned solid. Blocks the player horizontally while their feet are
 *  below `top`; if `standable`, its `top` also counts as ground to land on. */
export type Aabb = {
  minX: number
  maxX: number
  minZ: number
  maxZ: number
  top: number
  standable: boolean
}

/** The playground: a flat-floored room dropped into the center of a big open
 *  landscape. Geometry is split by texture, plus the collision solids, where the
 *  NPC stands, the heightfield the outdoor ground + player share, and the sky. */
export type Level = {
  floor: Mesh
  walls: Mesh
  crate: Mesh
  ground: Mesh
  colliders: Aabb[]
  npcPosition: { x: number; y: number; z: number }
  terrain: Terrain
  sky: SkyConfig
}

const ARENA = 12
const WALL_HEIGHT = 4
const CRATE = { x: -2, z: -2, half: 1, height: 1 }
/** Z-bias lifting the stone floor above the terrain skirt that laps under the
 *  room edge (see `buildLevel`). Big enough to beat depth precision, too small
 *  to see. */
const FLOOR_LIFT = 0.02

/** The world around the room: a flat clearing the size of the room (`inner`),
 *  rolling hills beyond, ramping into very high peaks at the `outer` rim ~20x
 *  the room across. Tune freely -- crank `peakHeight` for taller mountains,
 *  `outer` for a bigger world. */
const TERRAIN: Terrain = {
  inner: ARENA,
  outer: ARENA * 20,
  blend: 12,
  amplitude: 5,
  frequency: 0.14,
  peakHeight: 90,
  peakFrequency: 0.05,
  peakStart: 0.45,
}

/** Outdoor ground mesh resolution. A fixed grid over the whole world, so cell
 *  size (and cost) is set here, not by the world's size: bigger `outer` gives
 *  chunkier terrain, not more triangles. `GROUND_UV` sets texture tiles/unit. */
const GROUND_DIVISIONS = 56
const GROUND_UV = 0.25

/** The two cloud styles; swap which one the sky uses in `buildLevel`.
 *  `basicCumulus` is cheap flat puffs; `fancyCumulus` is the pricier
 *  heightfield-shaded, domain-warped version with faked volume. */
export const basicCumulus: CloudLayer = {
  kind: "basic",
  color: Color.rgb(248, 250, 255),
  coverage: 0.5,
  scale: 0.9,
  speed: 0.5,
  edge: 0.005,
}

export const fancyCumulus: CloudLayer = {
  kind: "fancy",
  color: Color.rgb(250, 251, 255),
  coverage: 0.5,
  scale: 0.6,
  speed: 0.5,
  edge: 0.02,
  warp: 0.4,
  relief: 7,
}

export function buildLevel(): Level {
  // Flat room floor, lifted a hair above the terrain's clearing (y 0). The
  // outdoor grid's cells straddle the room boundary and lap under the floor's
  // edges; this small z-bias keeps the flat stone floor winning the depth test
  // there instead of z-fighting the grass. The step is invisible at the doorway.
  const floor = mesh()
  const fy = FLOOR_LIFT
  quad(floor, [-ARENA, fy, -ARENA], [ARENA, fy, -ARENA], [ARENA, fy, ARENA], [-ARENA, fy, ARENA], 12, 12)

  // The big surrounding landscape, with a hole where the room sits.
  const ground = Terrain.ground(TERRAIN, GROUND_DIVISIONS, GROUND_UV)

  const walls = mesh()
  const h = WALL_HEIGHT
  // Three inward-facing walls; the north (-Z) side is left open onto the world.
  // No ceiling, so the sky shows above.
  quad(walls, [ARENA, 0, ARENA], [-ARENA, 0, ARENA], [-ARENA, h, ARENA], [ARENA, h, ARENA], 12, 2.5)
  quad(walls, [ARENA, 0, -ARENA], [ARENA, 0, ARENA], [ARENA, h, ARENA], [ARENA, h, -ARENA], 12, 2.5)
  quad(walls, [-ARENA, 0, ARENA], [-ARENA, 0, -ARENA], [-ARENA, h, -ARENA], [-ARENA, h, ARENA], 12, 2.5)

  // Crate on the flat room floor.
  const crate = mesh()
  box(crate, CRATE.x, CRATE.z, CRATE.half, 0, CRATE.height)

  const colliders: Aabb[] = [
    wall(-ARENA, ARENA, ARENA - 1, ARENA),
    wall(ARENA - 1, ARENA, -ARENA, ARENA),
    wall(-ARENA, -ARENA + 1, -ARENA, ARENA),
    {
      minX: CRATE.x - CRATE.half,
      maxX: CRATE.x + CRATE.half,
      minZ: CRATE.z - CRATE.half,
      maxZ: CRATE.z + CRATE.half,
      top: CRATE.height,
      standable: true,
    },
  ]

  const sky: SkyConfig = {
    zenith: Color.rgb(58, 108, 196),
    horizon: Color.rgb(178, 198, 226),
    sun: Color.rgb(255, 246, 214),
    sunDir: { x: 0.3, y: 0.5, z: -0.8 },
    sunSize: 0.04,
    clouds: basicCumulus,
  }

  const npcPosition = { x: 2, y: 0, z: -1 }

  return { floor, walls, crate, ground, colliders, npcPosition, terrain: TERRAIN, sky }
}

function mesh(): Mesh {
  return { vertices: [], indices: [] }
}

function wall(minX: number, maxX: number, minZ: number, maxZ: number): Aabb {
  return { minX, maxX, minZ, maxZ, top: WALL_HEIGHT, standable: false }
}

/** One flat quad (two tris). Corners run a (uv 0,0) -> b (us,0) -> c (us,vs) ->
 *  d (0,vs); `us`/`vs` set how many texture tiles span it. No subdivision is
 *  needed -- texturing is perspective-correct, so a single quad looks right at
 *  any size. */
function quad(m: Mesh, a: Corner, b: Corner, c: Corner, d: Corner, us: number, vs: number): void {
  const base = m.vertices.length
  m.vertices.push(
    { pos: { x: a[0], y: a[1], z: a[2] }, uv: { x: 0, y: 0 } },
    { pos: { x: b[0], y: b[1], z: b[2] }, uv: { x: us, y: 0 } },
    { pos: { x: c[0], y: c[1], z: c[2] }, uv: { x: us, y: vs } },
    { pos: { x: d[0], y: d[1], z: d[2] }, uv: { x: 0, y: vs } },
  )
  m.indices.push(base, base + 1, base + 2, base, base + 2, base + 3)
}

/** A box centered at (cx, cz), rising `height` units from `base`: top face plus
 *  four sides, one uv tile per face. No bottom (never seen). */
function box(m: Mesh, cx: number, cz: number, half: number, base: number, height: number): void {
  const x0 = cx - half
  const x1 = cx + half
  const z0 = cz - half
  const z1 = cz + half
  const y0 = base
  const y1 = base + height
  quad(m, [x0, y1, z0], [x1, y1, z0], [x1, y1, z1], [x0, y1, z1], 1, 1)
  quad(m, [x0, y0, z0], [x1, y0, z0], [x1, y1, z0], [x0, y1, z0], 1, 1)
  quad(m, [x1, y0, z1], [x0, y0, z1], [x0, y1, z1], [x1, y1, z1], 1, 1)
  quad(m, [x1, y0, z0], [x1, y0, z1], [x1, y1, z1], [x1, y1, z0], 1, 1)
  quad(m, [x0, y0, z1], [x0, y0, z0], [x0, y1, z0], [x0, y1, z1], 1, 1)
}